1. Field Of The Invention
The invention pertains to an improved fluid motor powered by a primary fluid stream in a pumping apparatus for injecting predetermined quantities of secondary fluid additive into a primary fluid stream.
2. Background Of The Prior Art
Several devices have been developed for injecting predetermined quantities of liquid additives into a primary liquid stream for such applications as adding medication to drinking water for livestock, treating water with additives such as halogens, or adding fertilizer concentrate to irrigation water, for example. In known devices, energy supplied to the pumping mechanism originates from the flow of the primary fluid under pressure in an enclosure containing a stepped differential piston. A mechanism with valves carried by the piston enables the fluid pressure to be applied to either face of the stepped piston, which thus describes a reciprocating motion and which forms the driving member for a metering piston interacting with a cylinder in communication with a storage vessel of the product to be injected. Such devices are found in my own U.S. Pat. Nos. 4,558,715 and 4,809,731, as well as U.S. Pat. No. 4,756,329 to Jean Cloup.
In conventional reciprocating fluid powered motors, a sliding shaft extends through the head of a differential stepped piston, usually through the center of the piston, and extends on both sides of the piston. The shaft is connected to a toggle mechanism and controls two sets of valves which alternately close fluid passages in one stepped piston face and open a flow passage or passages in the other stepped piston face. When the piston moves up or down in response to greater fluid pressure on one of the stepped faces, the upper or lower ends of the rod strike the housing causing the rod to stop moving while the piston continues to move. This causes relative sliding movement between the rod and the pressurized face of the piston requiring a seal therebetween to prevent the loss of pressure.
Conventional designs for these pump motors have a multitude of parts which are subject to stresses and wear and which decrease the ease of assembly, disassembly and maintenance. It would be desirable to have a more reliable rugged construction which the improved motor provides. In addition, the conventional toggle mechanisms are noisy, with parts assembled in such a way that it is very difficult to provide them a silencing means. It would be desirable to produce a quieter unit because pumping apparatus of this kind are frequently used in places where their noise in operation disturbs people in the surrounding area.
Air is often trapped in the upper chamber of the housing at start up and it would be desirable to provide a convenient way of bleeding the air to facilitate initiation of operation. It would also be desirable to have a way to stop the piston periodically without bypassing primary fluid around the motor.
Conventional apparatus employs extension springs having ends connected to parts which move away from the center in tension. These are disadvantageous because they are difficult to install or remove, and because the coils are tightly wound, the individual coils are difficult to process in secondary operations which could be used to make them more effective or protect them from a corrosive environment which is often present.